In a conventional photodetector for generating electric charges corresponding to a light amount received from a target space, and taking out information of the target space as a received-light output, a maximum value of the received-light output is generally restricted by the dimension of a portion for taking out the generated electric charges.
To expand dynamic range of a channel for taking out the generated electric charges, for example, it is proposed in Japanese Patent Early Publications No. 7-22436 and No. 7-22437 to remove undesired electric charges other than information signal in a charge transfer channel by use of a CCD, and use the remaining electric charges as effective electric charges. According to this configuration, since the undesired electric charges are not transferred, the charge transfer channel can be downsized by a reduction in charge transfer amount.
In this configuration, however, since the removal of the undesired electric charges is performed in the charge transfer channel, the so-called saturation phenomenon happens when the undesired electric charges generated by receiving the light from the target space exceed a photoelectric conversion capacity. In this case, there is a possibility that the information to be detected is lost prior to the charge transfer channel.
Therefore, according to the configuration of the above-described prior art, the charge transfer channel can be downsized. However, there is a problem that a photoelectric converting portion for receiving the light from the target space to generate the electric charges cannot be downsized.